From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Steve Wise" Subject: RE: [PATCH RFC] libibverbs: add ARM64 memory barrier macros Date: Thu, 19 May 2016 11:02:36 -0500 Message-ID: <060701d1b1e7$dc7e1ff0$957a5fd0$@opengridcomputing.com> References: <20160518220302.81260E09E9@smtp.ogc.us> <20160518222857.GB23835@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160518222857.GB23835-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> Content-Language: en-us Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: 'Jason Gunthorpe' Cc: dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rdma@vger.kernel.org > On Wed, May 18, 2016 at 02:16:39PM -0700, Steve Wise wrote: > > The default generic barriers are not correct for ARM64. This results in > > data corruption. The correct macros are lifted from the linux kernel. > > > > Signed-off-by: Steve Wise > > > > I wonder why the linux kernel doesn't export these? Also, if the hw > > platform is unknown, I don't think libibverbs should pick a default > > implementation that might cause data corruption. Rather, I think it > > should just fail a compile on that platform. > > These days, in user space this sort of stuff should be done following > the C11 atomic memory ordering model and not by trying to shoe-horn in > the kernel model. Then the compiler takes care of things properly. > > This is using calls like atomic_store, atomic_load and > atomic_thread_fence to create the same sort of barriers. > > You could probably implement the Xmbs() with variations on > atomic_thread_fence ?? Looking at the documentation, it is not clear to me which parameter value passed to atomic_thread_fence() maps to each of the mb services. Is it correct to think that if I get it right, the resulting assembly should be what we currently have for the mb services? Or perhaps someone else can provide guidance? Steve. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html